Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G47/00—Cracking of hydrocarbon oils, in the presence of hydrogen or hydrogen- generating compounds, to obtain lower boiling fractions
  • C10G47/02—Cracking of hydrocarbon oils, in the presence of hydrogen or hydrogen- generating compounds, to obtain lower boiling fractions characterised by the catalyst used
  • C10G47/10—Cracking of hydrocarbon oils, in the presence of hydrogen or hydrogen- generating compounds, to obtain lower boiling fractions characterised by the catalyst used with catalysts deposited on a carrier
  • C10G47/12—Inorganic carriers
  • C10G47/16—Crystalline alumino-silicate carriers
  • C10G47/18—Crystalline alumino-silicate carriers the catalyst containing platinum group metals or compounds thereof
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G2300/00—Aspects relating to hydrocarbon processing covered by groups C10G1/00 - C10G99/00
  • C10G2300/10—Feedstock materials
  • C10G2300/1096—Aromatics or polyaromatics
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G2300/00—Aspects relating to hydrocarbon processing covered by groups C10G1/00 - C10G99/00
  • C10G2300/40—Characteristics of the process deviating from typical ways of processing
  • C10G2300/4018—Spatial velocity, e.g. LHSV, WHSV

Definitions

• the present invention relates to a process for the catalytic hydrodealkylation of aromatic hydrocarbons.
• the present invention relates to a process for the catalytic hydrodealkylation of hydrocarbon compositions comprising Cs-Ci 3 alkylaromatic compounds mixed with C 4 -C 10 aliphatic and cycloaliphatic products. Even more specifically, the present invention relates to a process according to which the catalytic hydrodealkylation operates on alkylaromatic compounds present as such in the initial feedstock and on those produced under the same reaction conditions by the aromatization of aliphatic and cycloaliphatic compounds mixed together.
• concomitant transalkylation, isom- erization, disproportioning and condensation by-reactions are quantitatively suppressed.
• the process describes a hydrodealkylation of al- kylaromatic compounds which, on the basis of the reaction conditions and results shown, cannot be of a general type, but specific for an exclusive de-ethylation as the only alkylaromatic product which is de-alkylated is ethylbenzene. It is also known that, when a catalytic hydrodealkylation reaction takes place, the hydrogenated alkyl radical (methane, ethane, propane, etc.) which was subjected to catalytic dealkylation from the aromatic ring, must be found in gas phase.
• the hydrogenated alkyl radical methane, ethane, propane, etc.
• US patent 4,899,011 describes a process in which, once again, the evident objective is to isomerize a hydrocarbon feedstock containing paraffins and a Ce aromatic blend of ethylbenzene and xylenes, as the content of p-xylene is lower than that at equilibrium.
• the process includes the treatment of said feedstock under conventional reaction conditions, on a catalytic system with two fixed beds, in succession, each of them consisting of a zeolite catalyst of the ZSM-5 type, the first of which has a minimum crystal dimension of 1 ⁇ m whereas the second has dimensions lower than 1 ⁇ m.
• the zeolite can be modified by means of a noble metal selected from platinum, palladium or rhodium, or couples of noble metals such as platinum-rhenium, platinum- palladium or platinum-iridium, or terns of the platinum- iridium-rhenium type; or modified by means of the above noble metals and non-noble metals such as cobalt, nickel, vanadium, tungsten, titanium and molybdenum, to form couples of the platinum-nickel or platinum-tungsten type, or terns such as platinum-nickel-tungsten, even if the metal pre- ferred for the impregnation of the ZSM-5 is platinum.
• a noble metal selected from platinum, palladium or rhodium, or couples of noble metals such as platinum-rhenium, platinum- palladium or platinum-iridium, or terns of the platinum- iridium-rhenium type; or modified by means of the above noble metals and non-noble metals such as
• This patent includes the processing of said feedstock at a considerably lower pressure (lower than 14 bar) than those generally necessary in hydrodealkylation processes and with a molar ratio between hydrogen and ethylbenzene (1.2 mol/mol) even lower than those mentioned, for example, in US patents 4,482,773 (2- 2.2) and 4,899,011 (2.9-3), already much lower with respect to those which have to be used in order to obtain an effective hydrodealkylation, in the presence of a zeolite cata- lyst of the ZSM-5 type modified with platinum and magnesium.
• the catalytic hydrodealkylation of ethylbenzene proves to have a low efficiency and selectivity, under the reaction conditions and with the catalytic system used, consisting of a zeolite of the ZSM-5 type, in acidic form or exchanged with alkaline metals and treated with metals of group VIII, in particular platinum.
• the low efficiency is demonstrated by the low production of benzene and toluene, and by the significant amount of non-converted ethyl- benzene, whereas the poor selectivity is due to the intervention of transalkylation or disproportioning side- reactions, which lead to the formation of higher Cg + alky- laromatic products.
• US patent 5,689,027 claims a two-step process, in the first of which the operating conditions should be suitable for the hydrodealkylation of the ethylbenzene present in the feeding, whereas in the second step other operating conditions should promote the isomerization to p-xylene of the blend of isomers present in the feedstock which are not at equilibrium.
• the catalytic system used in both steps is a ZSM-5 zeolite exchanged with cations of alkaline or alka- line-earth metals, or treated with silanizing agents and subsequently activated with a metal selected from those belonging to group VIII, IB, IIIA and VA, particularly platinum, possibly coupled with tin.
• Patent WO 2005/071045 describes a process for the catalytic hydrodealkylation of hydrocarbon compositions comprising Ce-Ci 3 aromatic compounds, possibly mixed with C 4 -C 10 aliphatic or cycloaliphatic products, using a catalyst of the ZSM-5 type modified with metals selected among molybdenum, zinc, nickel, cobalt and palladium or couples of molybdenum-zinc and molybdenum-cobalt.
• the results claimed show an efficient dealkylation with good yields to benzene and toluene.
• the dealkylation of xylenes and C 9 -C 9+ initial aromatic compounds is, in any case, limited.
• the Applicant has now surprisingly found a process which allows the hydrodealkylation of C 8 -Ci 3 alkylaromatic hydrocarbons and, unexpectedly, also the contemporaneous catalytic hydrodealkylation of the alkylaromatic compounds obtained from the aromatization, under the same process conditions, as those initially present in a blend as C4-C10 aliphatic and cycloaliphatic hydrocarbons, to benzene, toluene and ethane (BTE) .
• the overall hydrodealkylation reaction takes place without concomitant transalkylation, dispropor- tioning, isomerization and condensation reactions which al- ways characterize the processes of the known art, by selecting suitable operative conditions and formulation of the zeolite catalyst.
• An object of the present invention therefore relates to a process capable of operating a selective catalytic hy- drodealkylation of hydrocarbon compositions comprising both a Cs-Ci 3 alkylaromatic fraction and a C 4 -Ci 0 aliphatic fraction which is contemporaneously aromatized under the process conditions.
• the process object of the present invention therefore allows the catalytic hydrodealkylation to be obtained of the aromatic C 8 -CiO fraction as well as the aroma- tization of the C 4 -Ci O aliphatic and cycloaliphatic fraction present, with subsequent instantaneous hydrodealkylation.
• said aromatic and aliphatic-cycloaliphatic hydrocarbon compositions are treated in continuous and in the presence of hy- drogen, using a catalyst consisting of a ZSM-5 zeolite car- rier, having a Si/Al molar ratio ranging from 5 to 100, modified by the couple of metals molybdenum and platinum (Pt-Mo) , at temperatures ranging from 400 to 650 0 C, preferably from 450 to 58O 0 C, at pressures ranging from 1 to 5 MPa (between 10 and 50 bar), preferably from 2.8 to 3.6 MPa (between 28 and 36 bar) , and with H 2 Zfeedstock molar ratios ranging from 1 to 10, preferably from 2 to 7, more preferably between 3.8 and 5.2.
• a catalyst consisting of a ZSM-5 zeolite car- rier, having a Si/Al molar ratio ranging from 5 to 100, modified by the couple of metals molybdenum and platinum (Pt-Mo
• the hydrocarbon feedstock subjected to hydrodealkylation comprises Cs-Ci 3 alkylaro- matic compounds, such as ethylbenzene, xylenes, di- ethylbenzenes, ethylxylenes, trimethylbenzenes, tetrame- thylbenzenes propylbenzenes, ethyltoluenes, propyltoluenes, butylbenzene, ethylxylenes, etc.
• Cs-Ci 3 alkylaro- matic compounds such as ethylbenzene, xylenes, di- ethylbenzenes, ethylxylenes, trimethylbenzenes, tetrame- thylbenzenes propylbenzenes, ethyltoluenes, propyltoluenes, butylbenzene,
• This feedstock can come from effluents of reforming units, for example, or from units which effect pyrolysis processes, such as steam cracking, and can contain a blend of aliphatic and cycloaliphatic C 4 -Ci 0 products which, under the process conditions, are aromatized and then hydrodealkylated.
• the lat- ter can be butanes, pentanes, hexanes, heptanes, etc.. and the corresponding cyclic and cycloalkylic derivatives (naphthenes) .
• the feedstock being fed can also contain het- eroatomic organic compounds, wherein the heteroatoms can be nitrogen, oxygen and sulphur, in the typical quantities generally present in feedstocks coming from reforming units or pyrolysis processes.
• the hydrocarbon feedstock used in the present process can, if required, be subjected to separation treatment, for example distillation or extraction, to concentrate the products to be subjected to subsequent hydrodealkylation. Furthermore, if required, the feedstock can be subjected to a previous hydrogenation to eliminate the unsaturations present in the aliphatic compounds and on the same alkyl substituents of the aromatic rings.
• hydrodealky- lation reaction conditions object of the invention in particular as a result of the amount of hydrogen used and the activity shown by the catalyst, it is possible to also contemporaneously obtain the direct hydrogenation of the unsaturated compounds present in the aro- matic feedstock to be hydrodealkylated, such as butenes, pentenes, alkylpentenes, cyclopentenes, alkylcyclopentenes, hexenes, alkylhexenes, cyclohexenes, alkylcyclohexenes, and so on, and other unsaturated naphthene compounds.
• the unsaturated compounds present in the aro- matic feedstock such as butenes, pentenes, alkylpentenes, cyclopentenes, alkylcyclopentenes, hexenes, alkylhexenes, cyclohexenes, alkylcyclohexenes, and so on, and other unsaturated naphthene compounds.
• Hydrogen itself allows the re- moval of sulphur, nitrogen or oxygen from the compounds typically present in hydrocarbon feedstocks, as these het- eroatoms are quantitatively removed (sulphur, for example, as H 2 S) .
• the hydrodealkyla- tion catalyst consisting on a ZSM-5 zeolite modified with the couples Pt-Mo of the metals platinum and molybdenum (Pt x -MO y ), surprisingly showed the highest selectivity to benzene, toluene and ethane (BTE) , with a quantitative reduction of xylenes and, above all, aromatic Cg-Cg + compounds (among Cg + products, particularly the heavy ones, such as naphthalenes and methylnaphthalenes) .
• Said catalyst moreover, allowed the underproduction of propane to be minimized, with the consequent simplification of the distillation/separation process from other valuable gases produced by the reaction, methane but, above all, ethane.
• the composition of the zeolite carrier must also have been of considerable help in obtaining such a good results.
• the lack of side-reactions, such as isomerization, transalkylation, condensation and disproportioning in the process object of the invention, is due to the reduction of the undesired acidity of the zeolite (ZSM-5) obtained with the amounts of aluminium found, particularly favourable with respect to silicon.
• ZSM-5 zeolite is available on the market or it can be prepared according to the methods described in literature (for example US patents 3,702,886 and 4,139,600).
• the structure ZSM-5 zeolites is described by Kokotailo et al. (Nature, Vol. 272, page 437, 1978) and by Koningsveld et al. (Acta Cryst. Vol. B43, page 127, 1987; Zeolites, Vol. 10, page 235, 1990) .
• the zeolitic catalyst is preferably used in bound form in the process of the present invention, adopting a binder which gives it form, consistency and mechanical resistance, so that the zeolite/binder catalyst can be used and suita- bly moved to an industrial reactor.
• binders suitable for the purpose include aluminas, such as pseudo- bohemite and ⁇ -alumina; clays, such as kaolinite, vermicu- lite, attapulgite, smectites, montmorillonites; silica; alumino-silicates; titanium and zirconium oxides; combina- tions of two or more of the above, used in such quantities as to give zeolite/binder weight ratios ranging from 100/1 to 1/10.
• the dispersion of the metals in the zeolite or zeolite/binder catalyst can be effected according to conven- tional techniques, such as impregnation, ionic exchange, vapour deposition, or surface adsorption.
• the incipient impregnation technique is preferably used, with an aqueous or aqueous-organic solution (the organic solvent preferably being selected from alcohols, ketones and nitriles or blends thereof) , containing at least one hydro- and/or or- gano-soluble compound of the metal, such as to assure a total final content of the metal in the catalyst ranging from 0.05 to 10% by weight, preferably from 0.5 to 4.
• the zeolite, with or without binder, is subsequently subjected to impregnation with metals to form the couple Pt x -MO y , wherein x and y represent the weight percentage of Pt and Mo, respectively. Thanks to this couple of metals, it was unexpectedly found that the performances of the reaction, with respect to the total conversion of the initial feedstock, capacity of contemporaneously aromatizing the aliphatic fraction present which is immediately hydrodeal- kylated and total selectivity to benzene, toluene and ethane (BTE) , proved to be exceptionally high.
• the impregnation comprises treating the zeolite, in or not in bound form, with the solutions of metals in succession or contemporaneously (co- impregnation) .
• the zeolite thus impregnated is dried and then calcined at temperatures ranging from 400 to 650 0 C. This operation can be repeated according to necessity.
• molybdenum compounds which can be used for this purpose are: molybdenum (II) acetate, ammonium (VI) mo- lybdate, diammonium (III ) dimolybdate, ammonium (VI) hepta- molybdate, ammonium (VI) phosphomolybdate and analogous salts of sodium and potassium; molybdenum (III ) bromide, mo- lybdenum(III) - (V) chloride, molybdenum (VI ) fluoride, molybdenum (VI) oxychloride, molybdenum ( IV) - (VI) sulphide, molyb- denic acid and the corresponding acidic salts of ammonium, sodium and potassium, and molybdenum (II-VI) oxides and others .
• platinum(II) chloride platinum(IV) chloride, platinum(II) bromide, platinum(II) iodide, platinum (IV) sulphide, chloroplatinic acid, ammonium hexachloro- platinate (IV) , ammonium tetrachloroplatinate (II) , potassium hexachloroplatinate ( IV) , potassium tetrachloroplatinate (II), sodium hexachloroplatinate (IV) hexahydrate, platinum(II) acetylacetonate, platinum (II ) hexafluoroaceti- lacetonate, dichloroethylenediamine platinum (II) tetramino nitrate and, in general, amine complexes of platinum(II) and (IV) , wherein the anions can be halides, sulphate, nitrate, n
• the catalyst obtained is Pt x -Mo y /ZSM-5, with a total metal content ranging from 0.05 to 10% by weight, preferably from 0.5 to 4% by weight.
• Said catalyst is charged into a fixed-bed reactor fed in continuous with the hydrocarbon feedstock and hydrogen.
• the selection of the flow-rate of the reagents is also absolutely important for obtaining a selective hydrodealkylation of the C 8 -Ci 3 aromatic hydrocarbons and the C 4 -C 10 aliphatic/cycloaliphatic hydrocarbons present in a blend and contemporaneously aromatized.
• the feeding flow-rates of the hydrocarbon mix and hydrogen must be such as to guarantee a LHSV (Liquid Hourly Space Velocity) , calculated with respect to the hydrocarbon stream, ranging from 3 to 5 h "1 , more preferably from 3.5 to 4.5 h "1 .
• LHSV Liquid Hourly Space Velocity
• the molar ratio between hydrogen and the feedstock fed must remain within the range of 1 and 10 mol/mol, more preferably between 2 and 7 mol/mol, even more preferably between 3.8 and 5.2 mol/mol.
• the experimental equipment used comprise a tubular fixed-bed reactor made of stainless steel, with an inner diameter of 20 mm and total height of 84.5 cm with an electric heating oven which forms jackets the reactor.
• the liq- uid feedstock is fed to the reactor by means of a high pressure pump.
• the gaseous reaction effluent is cooled by means of a quench device followed by a gas-liquid separator.
• the isothermal section of the reactor maintained at a constant temperature by automatic control, is charged with the catalyst.
• This system favours the achievement, in very short times, of isothermal conditions, not limited to the fixed-bed alone, but which are established along the whole reactor allowing an easier and more precise control of the operating temperature of the catalyst.
• the liquid and gaseous effluents produced by the reaction are separated downstream of the reactor and analyzed by gas chromatography at intervals .
• a catalyst A is prepared, which is obtained by mixing a ZSM-5 zeolite having a Si/Al molar ratio of 30 and an alumina as binder, the two phases being in a 60/40 weight ratio, and extruding the mixture.
• the extruded product is calcined in air at 550 0 C for 5 hours and its BET surface area is 290 m 2 /g. Once this has reached room temperature, it is crushed and sieved to produce a powder having dimension ranging from 20 to 40 mesh (between 0.84 and 0.42 mm), so that 12.4 g of catalyst powder occupy an equivalent volume of 20 ml.
• Catalyst B comparative
• Catalyst B is obtained by impregnating the catalyst A (30 g) with an aqueous solution (35 ml) containing 0.6 g of tetramino platinum nitrate (NH 3 ) 4 Pt (NO 3 ) 2 at about 25°C for 16 hours and, subsequently, placed under a nitrogen flow for 12 hours, dried in an oven at 120 0 C for 4 hours under vacuum and calcined in air at 550 0 C for 5 hours.
• Catalyst C is obtained by impregnating the catalyst A (50 g) with an aqueous solution (60 ml) containing 0.92 g of ammonium molybdate [NH 4 ) 6 Mo 7 O 24 .4H 2 O] and then following the procedure used for preparing catalyst B.
• the content of molybdenum in the catalyst was calcu- lated as being 1.0% by weight, with respect to the value of 1.05% by weight determined by means of ICP-MS analysis.
• Catalyst D is obtained by impregnating catalyst A (50 g) in two steps: a first impregnation with an aqueous solution (60 ml) containing 0.69 g of ammonium molybdate, followed by a second impregnation with an aqueous solution (50 ml) containing 0.25 platinum tetramino nitrate.
• the impregnation procedure with the first metal is effected as de- scribed for catalyst B, but without calcination, followed by impregnation with the second metal with the same operative procedures, followed by the final calcination in air at 550 0 C for 5 hours.
• the molybdenum and platinum content in the catalyst was calculated as being 0.75% by weight and 0.25% by weight, respectively, compared with the values of 0.76% by weight and 0.23% by weight obtained by ICP-MS.
• the order of impregnation with the metals can be inverted.
• Catalyst E is obtained by impregnation of catalyst A (20 g) in two steps: a first impregnation with an aqueous solution (24 ml) containing 0.19 g of ammonium molybdate, followed by a second impregnation with an aqueous solution (23 ml) containing 0.2 g of platinum tetramino nitrate.
• the impregnation procedure with the two metals is effected as described for catalyst D.
• the impregnation order can be inverted.
• the molybdenum and platinum content in the catalyst was calculated as being 0.5% by weight and 0.5% by weight, respectively, compared to the values of 0.52% by weight and 0.49% by weight, respectively, determined by ICP-MS.
• Catalyst F is obtained by impregnation of catalyst A (20 g) in two steps: a first impregnation with an aqueous solution (24 ml) containing 0.10 g of ammonium molybdate, followed by a second impregnation with an aqueous solution
• the impregnation procedure with the two metals is effected as described for catalyst D.
• the impregnation order can be inverted.
• the molybdenum and platinum content in the catalyst was calculated as being 0.25% by weight and 0.75% by weight, respectively, compared with the values of 0.26% by weight and 0.73% by weight obtained by ICP-MS.
• Example 1-6 (1-3 comparison)
• the reactor is charged with 20 cm 3 (12.4 g) of catalyst A, whereas the rest of the volume is filled with corundum in granules, in order to guarantee optimum distribu- tion and mixing of the gaseous flow of reagents and of the heat supplied to the reaction.
• a feedstock whose composition is indicated in the following Table 1, is fed to the reactor, suitably mixed with hydrogen and pre-heated to 280° C.
• the reaction is carried out at a pressure of 3 MPa, with a reagent feedstock flow-rate which is such as to obtain a LHSV of 3,9-4.1 h "1 , and a H 2 /feedstock molar ratio of 4.5.
• the concentration of toluene shown in Table 2 is the net concentration produced by the reaction.
• the hydrodealkylation reaction carried out at a temperature of 550 0 C shows how the presence of one of the two metals, molybdenum or platinum, in the ZSM-5 (Examples 2 and 3) favours the selective dealkylation of aromatic compounds, inhibiting the side-production of methane in favour of that of ethane, with respect to the reaction carried out with the catalyst as such (ZSM-5, Example 1).
• the production of benzene and toluene is also increased and their ratio (benzene/toluene) becomes favourable to benzene.

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